1. Field of the Invention
This invention relates to an ophthalmic illumination apparatus, and particularly to improvements in the illuminating optical system of a microscope for operation, and more particularly to an apparatus for protecting the tissue of the fundus of an eye from excessive illuminating light.
2. Related Background Art
In recent years, operations for cataracts have been widely performed and microscopes for operation are requisite during operation. However, the illuminating light of microscopes for operation is very great in its intensity and the time for operation is relatively long and therefore, the tissue of the fundus of an eye may be injured by rays of light which have entered from the pupil of an eye to be examined.
For this reason, various propositions have heretofore been made to protect the tissue of an eye from the excessive illuminating light of a microscope for operation.
For example, Japanese Patent Application Laid-open No. 60-111625 discloses a technique of disposing a light absorbing layer in a plane in the central area of an illuminating optical path which is conjugate with an object surface, and inserting the light absorbing layer into an illuminating optical system as required.
In the above-described apparatus according to the prior art, however, the illuminating light is all shaded by the light absorbing layer. This has led to the inconvenience that even when more or less brightness is necessary in a portion to be treated as in the suturing treatment during an operation, the portion to be treated becomes too dark due to the light absorbing layer and the operation becomes difficult.
Also, the light absorbing layer which is a shading member, must be mechanically mounted and dismounted. This has led to the inconvenience that each time the shading operation is performed, vibration is created, and as a result, the vibration is also transmitted to the microscope.
Further, the shape of the light absorbing layer cannot be changed. This has led to the inconvenience that the apparatus cannot cope with any variation in the size of the pupil of an eye to be examined.